Pressure controlled system



Dec. 2s, 1943. R. BENNETT 2,338,021

PRESSURE CONTROLLED SYSTEM Fl'ed Feb. 8, 1941 3 Sheets-#Sheet l.

Dec 28, 1943. R. BENNETT f 2,338,021

FRESSURE CONTROLLED SYSTEM Filed Feb. 8, 1941 3 Sheets-Sheet 2 wlw Illl M ,vuenon ZOLA No BENNETT De.2s,1943. R BENNETT 2,338,021

PRESSURE CONTROLLD lSYSTEM Filed Feb. 8, 1941 3 Sheets-Sheet 5 Patented Dec. 28, 1943 UNIT STATES FEC Applicationliebruary 8, 1941, Serial No. 373,09l In Great Britain February 10,1940

l Claims.

This invention relates toapparatus for controlling systems in which fluid has to lce supplied at a pressure that does not deviate from a predetermined vaiue except within small and well defined limits.

According to the present invention, a controlled member is arranged to compensate for any changes in pressure in a main fluid system in accordance with variations in the pressure exerted by the system on a .diaphragm controlling avalve which, in turn, controls the pressure of a fluid column interposed between the valve and the controlled member. Thus, the arrangement is in the nature of a hydraulic amplier, such that a slight deflection of the diaphragm due to a slight change in the pressure of the main fluid system causes a comparatively large movement of the controlled member, andv this in turn causes the necessary correction of the pressure in the main system. The valve may have a pair of pistons between which the iluid for the fluid column, which may loe said to constitute a secondary fluid system, is admitted under pressure, and 'this fluid may be received from the main system.

In order that the invention may be clearly understood and readily carried into effect, apparatus in accordance thereby will now be described, by of example, with reference to :le accompanying drawings, in which- Figurel is a diagrammatic sectional elevation of one form of apparatus,

Figure la is a diagram showing the manner which the apparatus on Figure l is made use of practice, and

Figure 2 is a diagrammatic elevation partly section of a further form of apparatus.

The apparatus in Figure 1 comprises a reducing valve having opposed pistons l and controlling the pressure in a column of fluid contained .in a space "i, a pipe 8 and the upper end ci a cylinder it. The latter contains a controlled mer in the form oi a piston it on the remote side of which a compression spring it acts. The piston Il is formed so as to act as a valve for admitting huid under pressure to the space l', and when the system is in equilibrium a small quantity oi fluid passes the piston to the space l, this quantity being equal to the amount of fluid that leaks from the fluid column through a port to a discharge pipe lil, The quantity ci iluld that can leak through the port il may oe adiusted manually through the medium ci a set screw t .having a tapered end a.

When the piston lil is to he moved to a new position against the action of the compression in in spring it, the pistons l and 2 are moved downwards (as viewed in Figure l) so as to increase the rate at which the uid enters the fluid column. When, however, the piston il is to be moved in the opposite direction by the spring it, the pressure in the fluid column is reduced ny allowing the pistons i and i. to move upwards so that the quantity ci fluid entering the space 'I less the quantity oi fluid escaping throughl the port t. The means for adjustingthe position ci the pistons l and 2 comprise a diaphragm lil, the upper surface of which closes a space comprising a pipe il leadingv to a space l between the pistons l and 2.

A pipe l2 connects the space l with a delivery pipe ia (Figure la) leading from a pump P that is to deliver fluid at a substantially constant pressure along pipe ita to the point Q where such fluid is required. This pump P is oi the type (well known in' the art) that has a variable stroke, and the apparatus appearing in Fig. l of this specification serves the purpose of controlling the stroke oi the pump in such a way as to compensate for any `variations in the pressure ol the pump output.

it will be seen that the diaphragm lll bears upon the upper end of the piston i, which is of considerable length and which slides in a cylinder 5 that constitutes a co-axial extension ofthe space i which', in turn, is constituted hy the upper end of the cylinder in which the piston 2 slides. The piston 2 has a larger diameter than the piston i, and a rod 3 connects the two pistons so that an integral piston unit is provided. The piston 2' carries a head 2a which can bear against an annular projection 2b in the space i so as to prevent any iuid under pressure from passing between the spaces 4i and l. When, however, the head la' is separated from the projection 2li, iluid under pressure passing through slots il, formed parallel to the piston axis along the curved surface of the piston 2, can enter the space l.

When the system is in equilibrium, there is no resultant force tending to move the pistonsl l and 2 axially. The resultant downward torce due to the pressure between the pistons i and E togather with the pressure upon the diaphragm it being balanced' by the upward pressure upon the piston Z and the iorce due to the strain in the diaphragm itself.

Now supposing that there is a small but undesirable increase in the output pressure of the pump P (Figure la) this results in an increase in the pressure of the fluid contained in the pipes lia, i2 and Ii, the space 4 and the space immediately above the diaphragm It. The diaphragm Hl, therefore, is further stressed and strained to a greater extent so that it pushes the pistons l and 2 downwards a small amount with the result that the quantity of fluid entering the space 'l is greater than the quantity leaking through the port 9. The pressure in the duid column consequently increases and the piston I4 is pushed downwards against the action of the spring l5, a piston valve 2li connected by a piston rod to the piston lil being also moved downwards. This piston valve 24 forms part oi servo-mechanism for controlling the stroke of the pump P, the control being elected through the medium of a piston (il) connected to the pump by a piston rod Si and a lever 6ta (Figure 1a) The piston valve 24 slides in a sleeve Ei which in turn can slide in a cylinder i3d, the interior of which is separated from the interior of cylinder i3 by a plate d3 which serves as the abutment necessary for the end of the spring it remote from the piston lf3. When the piston valve 2@ is moved downwards as aforesaid, fluid under pressure passes from a pipe i! through ports 59a and 55d, formed in the sleeve and a pipe 5l to the lower end of a cylinder which contains the piston Fluid above the piston 5i) can escape from the cylinder Si. through a pipe t2, ports 52d, formed in the sleeve 56, and an exhaust pipe 54.

In order that the piston @il shall move to a position corresponding to the position of the piston valve it is necessary for the supply of fluid under pressure to the cylinder 52 to be cut o'l after a short time correspondingr to the distance through which the piston valve 534 has been moved. This cut-on is effected through the medium of the sleeve titi which is caused by the piston to follow the piston valve 25.1 until the ports 51a and 52o are again closed. The connection between the sleeve 55 and the piston 6! is constituted by a lever 6.6, pivoted about a iiXed axis 65, and a link t6. The lever Ef! carries a pin lil that lies in a transverse slot Gil formed in the piston rod iii. Thus, when the piston Ell moves upwards, the slot G8 acts on the pin S1 to swing the lever Cid in a counter-clockwise direction and pull the sleeve 5'5 downwards until the fluid supply to the cylinder 62 is cut off and the movement oi the piston El@ consequently ceases.

When there is a slight decrease in the pressure on the delivery side of the pump, the pressure above the diaphragm il! is correspondingly reduced so that the pressure acting upwardly on the pistons l and 2 can lift these pistons slightly and thereby reduce the pressure above the piston lil on account of the lack of compensation for the leakage that taires place through the port 9. The spring lf3, therefore, moves the piston lll upwards, es well as the piston valve tifl. Accordingly, fluid under pressure passes from a pipe 59 through ports 5ta and formed in the sleeve to the pipe which leads to the upper end of the cylinder dil. The piston til is therefore urged downwards, whilst exhaust from the cylinder passes through the pipe 5i and the ports and 53a to the exhaust pipe After a predetermined time the ports ild and 52d are closed as a result of the upward movement of the sleeve 56, caused by the piston rod acting through the lever and the link It will be seen, therefore, that, when the pressure in pipes 52a, l and il increaseathe stress in the diaphragm I0 is increased and the piston 60 is moved downwards and thereby, through the rod 8| and lever Sla, decreases the stroke of the pump P to decrease the pressure in the pipe l2a and compensate for the increase in pressure which effected the movement. On the other hand, when the pressure above the diaphragm I0 decreases so that the piston 6i! is caused to descend, as viewed in Figure 1, the stroke of the pump P is increased and the pressure in the pipe l2 is increased.

Figure 2 shows the manner in which the mechanism in the upper part of Fig. 1, that is to say the mechanism comprising the pistons l and 2 and the diaphragm I0, may be used in conjunction with a throttle valve to maintain constant the pressure of duid passing through a conduit. In this arrangement, the pipe 8 leading from the space ll is connected to the upper end of a cylinder I3?) containing a piston leb loaded by a compression spring Ib. The action of the piston Mb and spring lb is precisely similar to the action of the piston M and spring IS in Figure 1. The outlet side 69 of the throttle-valve l0, which is a balanced throttle-valve of standard construction, is in communication through the pipes il and i2 with the top of the diaphragm lll. IThus, when there is an undesired increase in pressure, the diaphragm l0 is deected downwardly and there is a corresponding movement of the piston i413. This results in the throttle-valve 'lil being moved downward so as to reduce the pressure on the outlet side of the valve. Alternatively, when there is an undesired decrease in pressure on the outlet side of the valve, the throttle-valve l0 is caused to rise.

The pressure responsive apparatus may be used to control contrivances other than a variable stroke pump or a throttle-valve, for example the apparatus may be used in conjunction with a variable speed gear driving a chain grate stolrer, or a variable baille controlling the draught from a furnace.

It will be seen that in each example described above the fluid pressure acting on the diaphragm Hl constitutes an adjustable loading means, and when the pressure on the diaphragm l@ is slightly increased to cause a small increase in the strain in and, therefore, the defiection of the diaphragm, the pistons l and 2 are moved a small distance to increase the rate at which :duid is supplied past the valve elements 52a, 2b and to the uid column contained in the space l, the pipe 8 and the space above the piston M or lith. Thus, fluid is admitted to the column from the space between the pistons I and 2 at a greater rate than the rate at which the fluid is discharged from the column through the bleeder port 9. The pressure in the fluid column, therefore increases until a new condition of equilibrium is reached and the piston i4 or llh is moved by this increase in pressure, whilst the spring it or lh is compressed. Clearly, the movement of the piston ill or Ulli, which constitutes the controlled member, is very considerably greater than the deflection of the diaphragm which causes such movement and the comparatively large movement of the controlled member ld or lh causes the necessary correction of the pressure in the pipe lila in which the pressure is to be maintained substantially ccnstant. The diaphragm l t? is continuously strained by the pressure above it and it is the slight changes in strain due to slight changes in the pressure above it that bring about the controlling movements of the pistons l and 2.

When the new condition of equilibrium is being reached, in which condition the piston I or |419 has been moved downwards against the spring I6 or IBb, the increase in pressure in the iluid column in pipe 8, space 'I and the space above the piston I4 or I4b causes the pair of pistons I and 2 to return very nearly to its initial position and the small increase in the strain in or deilecticn of the diaphragm IB very nearly to vanish, the slightly increased pressure on the diaphragm being balanced by the increased tension in the diaphragm and the increase of pressure acting upwards on the larger of the two pistons I and 2, that is on the piston 2. There is then equilibrium between, on the one hand, the force due to the pressure on the diaphragm IB together with the resultant force due to the pressure between the two pistons I and 2 and, on the other hand, the force due to the pressure in the fluid column up.- on the larger one of the two pistons and the force due to the stress in the diaphragm I0. The stress in the diaphragm itself counterbalances most of the load due to the pressure on the diaphragm. It has been found that when once a condition of equilibrium has been reached, the pistons I and 2 undergo no perceptible movement and their positions depend upon the rate at which the bleeder port 9 permits the escape of fluid from the column in the space 1, the pipe 8 and the space above the p-iston I4 or Illb. This rate of escape in the equilibrium condition is the same as the rate at which fluid enters the column between the valve elements 2a and 2b. It may be mentioned that the changes in the deflection of the diaphragm are practically imperceptible, so that, while the position of the piston III or |41) is being changed, there is scarcely any perceptible departure of the diaphragm I from its normal deflection or strain under the predetermined pressure to be kept constant in the pipe I2a.

If the sizes of the parts are properly chosen, the pressure in the constant pressure system in the pipes I2a, I2 and II can be kept automatically within small and Well defined limits and, in calculating the dimensions, the known theory relating to small strains in a circular plate clamped at its edge is made use of. It can, in fact, be shown that the percentage pressure variation that can occur in the constant pressure system is a function only of the diameters of the small piston I and of the diaphragm I0. This result is arrived at by equating the additional small deflection of the diaphragm I0 that would occur, on account of a small increase of the fluid pressure distributed over its upper surface, to the opposing deflection that would occur as a result of the increased pressure on the inner face of the smaller piston I which is open to the constant pressure system contained in pipes I2a, I2 and I I.

I claim:

l. Pressure responsive apparatus comprising, in combination, means, including rigid walls and a diaphragm plate rigidly fixed around its edge to said walls, defining a space adapted to communicate with a source of fluid under pressure, a reciprocable member formed with a valve element and with spaced opposed piston faces of different areas adapted to receive fluid under pressure therebetween, said member being continuously in operative association with the centre of said diaphragm to follow movements thereof during the operation of the apparatus, a container formed with a bleeder port, guiding means for said reciprocable member, said guiding means being formed with a passage adapted to connect the space between said piston faces with the source of fluid under pressure and said valve element being adapted to vary the flow of fluid under pressure from said space between said pistons to said container, and means responsive to pressure changes in said container for controlling the pressure of the source of uid under pressure, the pressure in said container varying in accordance with the relation between the continuous flow past said Valve element into said container and the continuous ilow through said bleeder port out of said container.

2. Pressure responsive apparatus comprising, in combination, a chamber in communication with fluid under pressure, a second chamber having a controlled bleeder port therein, a valve controlling flow of fluid from the first chamber to the second chamber, means responsive to a predetermined pressure in the first chamber for opening said valve to permit fluid to flow into said second chamber faster than it can escape from said second chamber through said bleed port, means for supplying fluid under pressure to said rst chamber, and means responsive to pressure in said second chamber for controlling said pressure producing means.

3. Pressure responsive apparatus comprising, in combination, a chamber in communication with fluid under pressure, a second chamber having a controlled bleeder port therein, a valve controlling flow of fluid from the iirst chamber to the second chamber, means responsive to a predetermined pressure in the rst chamber for opening said valve to permit uid to flow into said second chamber through said bleed port, means for supplying fluid under pressure to said first chamber, means responsive to pressure in said second chamber for controlling said pressure producing means, a cylinder in communication with said second chamber, a controlled piston reciprocable in said cylinder and responsive to the pressure in said second chamber, a reaction spring acting on said controlled piston, and a throttle valve actuated by said controlled piston for controlling the pressure of the source of uid under pressure.

4. Pressure responsive apparatus comprising, in combination, a chamber in communication with fluid under pressure, a second chamber having a controlled bleeder port therein, a valve controlling flow of uid from the rst chamber to the second chamber, means responsive to a predetermined pressure in the rst chamber for opening said valve to permit iiuid to flow into said second chamber faster than it can escape from said second chamber through said bleed port, means for supplying iiuid under pressure to said first chamber, means responsive to pressure in said second chamber for controlling said pressure producing means, and a cylinder in communication with said second chamber, a controlled piston reciprocable in said cylinder, a reaction spring acting on said controlled piston, fluid operated servo-mechanism actuated by said controlled piston, and means responsive to said servo-mechanism for adjusting the pressure of the source of fluid under pressure.

ROLAND BENNETT. 

